The present disclosure relates generally to the field of refrigeration systems. More specifically, the disclosure relates to pump control in a refrigeration system. More particularly, the disclosure relates to a system and method for controlling the operation of pumps that circulate a secondary coolant to the temperature controlled storage devices of a refrigeration system.
It is known to provide a refrigeration system including a refrigeration device or temperature controlled storage device such as a refrigerated case, a refrigerator, a freezer, etc. for use in commercial and industrial applications involving the storage and/or display of objects, products and materials. For example, it is known to provide a refrigeration system with one or more refrigerated cases for display and storage of frozen or refrigerated foods in a supermarket to maintain the foods at a suitable temperature (e.g., 32 to 35 degrees F.). In such applications, refrigeration systems often are expected to maintain the temperature of a space within the refrigerated case where the objects are contained within a particular temperature range that is suitable for the particular objects, typically well below the room or ambient air temperature within the supermarket. These refrigeration systems will typically include a heat exchanger in the form of a cooling element or loop within the refrigeration device and provide a flow of a fluid such as a coolant into the cooling element to refrigerate (i.e., remove heat from) the space within the refrigeration device. The refrigeration systems may also include sensors such as thermometers (or thermoswitches) and some type of control system (or timer) configured to provide for the regulation of the target temperature range within the refrigerated case. Various types or configurations of refrigeration systems (e.g., direct expansion system and/or secondary system, etc.) may be used to provide the target temperature range.
In refrigeration systems having a primary loop that circulates a direct expansion type refrigerant that interfaces with, and cools, a liquid coolant in one or more secondary loop(s), the coolant flows through the cooling loops by way of one or more pumps, for example multiple variable speed pumps. The speed of the pump may be adjusted to provide more or less pressure of the coolant in the coolant loops. The adjustment of the pressure of the coolant in the secondary coolant loops as it relates to a hydronic system directly relates to a flow rate adjustment; thus measured pressure within the system is indicative of a required flow rate and hence a cooling requirement. The ability to adjust the flow of coolant to match the cooling requirements of the loads (e.g., temperature controlled cases, etc.) that are connected to each secondary coolant loop is intended to improve management of energy consumption, to obtain improved temperature control in the cases, and to reduce wear on system components. One algorithm for controlling the pump speed is by loop averaging. Loop averaging calculates a mean of measured pressure values from the coolant loops and adjusts the pumps based on the average value.